This project was initiated to study the role of brain neuropeptides in genetic hypertension and stress and has now been extended to study the interrelationship between different neuropeptides and their role in neuroendocrine regulation. Genetically hypertensive rats show changes in vasopressin and somatostatin metabolism when submitted to stress, and a naloxone-reversible and propranolol reversible decrease in pain sensitivity. Angiotensin-converting enzyme (ACE) activity is heterogeneously distributed in the CNS. There are changes in hypothalamic and posterior pituitary ACE activity in rats lacking vasopressin, changes in which are reversible after vasopressin replacement.